You can undo the last change by clicking on the button <Undo>
. Click by click you can undo all changes until you reach the last entry of an absence. An absence by itself cannot be undone. If you want to cancel an entry of an absence then you have to delete it.

The "Undo List" displays all changes since the last entry of an absence. To delete several entries at once, place the cursor in the line to which all changes shall be deleted, then click on the button <Undo>.